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A Closer Look at the Dynamical State of the High-redshift Galaxy Cluster SPT-CL J2215-3537

Vinicius S. Bessa, Renato A. Dupke, Yolanda Jiménez-Teja

Abstract

We present a comprehensive reanalysis of the dynamical state of the high-redshift galaxy cluster SPT-CL J2215-3537 (z = 1.16), using the full set of available Chandra observations to characterize the thermodynamic and morphological properties of the intracluster medium. Although previously identified as one of the most distant dynamically relaxed systems based on X-ray morphological statistics, we find compelling evidence that SPT-CL J2215-3537 displays some level of dynamical activity. This includes temperature anisotropies consistent with the first detection of a pair of core-sloshing cold fronts at z > 1. We identify a ghost cavity candidate and estimate its mechanical power as log10(Pcav/10^42 erg s^-1) = 2.66 +- 0.23, confirming that radiative cooling strongly exceeds active galactic nucleus feedback heating. We show that SPT-CL J2215-3537 is likely in a short transient phase preceding the onset of a self-regulated cooling-feedback cycle. We recalculate traditional X-ray morphological parameters and discuss how non-self-similar evolution of parameters sensitive to the surface brightness cuspiness can bias dynamical classifications at high redshift.

A Closer Look at the Dynamical State of the High-redshift Galaxy Cluster SPT-CL J2215-3537

Abstract

We present a comprehensive reanalysis of the dynamical state of the high-redshift galaxy cluster SPT-CL J2215-3537 (z = 1.16), using the full set of available Chandra observations to characterize the thermodynamic and morphological properties of the intracluster medium. Although previously identified as one of the most distant dynamically relaxed systems based on X-ray morphological statistics, we find compelling evidence that SPT-CL J2215-3537 displays some level of dynamical activity. This includes temperature anisotropies consistent with the first detection of a pair of core-sloshing cold fronts at z > 1. We identify a ghost cavity candidate and estimate its mechanical power as log10(Pcav/10^42 erg s^-1) = 2.66 +- 0.23, confirming that radiative cooling strongly exceeds active galactic nucleus feedback heating. We show that SPT-CL J2215-3537 is likely in a short transient phase preceding the onset of a self-regulated cooling-feedback cycle. We recalculate traditional X-ray morphological parameters and discuss how non-self-similar evolution of parameters sensitive to the surface brightness cuspiness can bias dynamical classifications at high redshift.
Paper Structure (4 sections, 6 equations, 3 figures)

This paper contains 4 sections, 6 equations, 3 figures.

Table of Contents

  1. Introduction
  2. X-Ray Spectral Analysis
  3. Radial Thermodynamic Profiles
  4. Projected Thermodynamic Maps

Figures (3)

  • Figure 1: Top: Deprojected electron density profile. The blue dots were obtained from Equation \ref{['eq:ne']}, while the red curve corresponds to the $\beta$-model applied to the surface brightness profile, whose optimal parameters are inserted in Equation \ref{['eq:nbet']}. Bottom: residual between the data and the model. The sharp decline observed in both the density profile and the residual around $r_{\mathrm{sharp}} \approx 160$ kpc / $19.4$ arcsec is associated to two symmetric cold fronts.
  • Figure 2: Radial profiles of various 3D thermodynamic quantities: (a) Temperature ($kT$), (b) Pressure ($P$), (c) Entropy ($K$), and (d) Cooling Time ($t_c$). The shaded region in (d) indicates the cooling radius $r_{cool}$. The dotted vertical line in all panels mark $r = 160$ kpc to indicate the approximate projected radius of the observed discontinuity.
  • Figure 3: Projected thermodynamic maps (temperature, pseudo-entropy, and pseudo-pressure) derived using WVT adaptive binning followed by kriging interpolation, along with the corresponding lower and upper residual error maps. White ellipses in the temperature map indicate the approximate locations of colder clumps. The red cross marks the position of the BCG. Coordinates are shown as offsets from the BCG in arcseconds ($1 \text{ arcsec}= 8.25 \text{ kpc}$).